This acronym stands for "Perfect Site Integration." There are times in a session when the contact with the site is so strong that the Viewer experiences actual presence at the site. Full sound, sight, tactile, smell, and all other sensory impressions are as they would be if the Viewer were actually there. This is extremely rare, and most exciting because it seems to the viewer that he/she is actually at the site.
In formal CRV, it is also discouraged, because while the viewer it experiencing the site totally, he/she is unable to report the experiences. Therefore, when he/she "comes back" from the site, all that gets reported is a pale summary of impressions. CRV developers found that keeping a viewer slightly detached from the site and reporting perceptions as they happen gives much more complete and accurate information.
See also, "bilocation".